The present invention relates to refrigeration systems and, more particularly, to methods of operating and control systems for refrigeration systems such as centrifugal vapor compression refrigeration systems.
Generally, refrigeration systems include an evaporator or cooler, a compressor, and a condenser. Usually, a heat transfer fluid is circulated through tubing in the evaporator thereby forming a heat transfer coil in the evaporator to transfer heat from the heat transfer fluid flowing through the tubing to refrigerant in the evaporator. The heat transfer fluid chilled in the tubing in the evaporator is normally water which is circulated to a remote location to satisfy a refrigeration load. The refrigerant in the evaporator evaporates as it absorbs heat from the water flowing through the tubing in the evaporator, and the compressor operates to extract this refrigerant vapor from the evaporator, to compress this refrigerant vapor, and to discharge the compressed vapor to the condenser. In the condenser, the refrigerant vapor is condensed and delivered back to the evaporator where the refrigeration cycle begins again.
Normally, sensors are provided in refrigeration systems of the type described above to sense certain refrigeration system operating conditions during normal operation of the refrigeration system. These sensors provide signals indicative of the sensed operating conditions to a control system for the refrigeration system. For example, a flow sensor may be provided to sense flow of the heat transfer fluid through the tubing in the evaporator. The control system controls various operating parameters of the refrigeration system or takes various safety control actions in response to the sensed operating condition. For example, the control system may shut down operation of the refrigeration system to prevent freezing of the heat transfer fluid in the tubing in the evaporator if no flow is sensed by the flow sensor in the tubing in the evaporator.
Operating condition sensors in refrigeration systems of the type described above must provide accurate, reliable indications of the sensed operating conditions if the refrigeration system is to operate properly. This is especially true of safety sensors to avoid needless shutdowns of the refrigeration system due to faulty sensors or faulty readings provided to the control system by the sensors.